A variety of different gate valves have been in use for many years. Typically a gate valve has a flat steel or cast sliding plate or gate which closes against a seat to shut off a flow of material, liquid or gas. Most gate valves are used with liquids although some are used with dry materials.
Flap gate valves are normally used with dry materials and such valves are described in my prior U.S. Pat. Nos. 4,480,812, 4,498,492, 4,308,894, 3,410,422 and 3,257,045, assigned to the assignee of this invention. Flap gate or flap valves used in conveying dry materials have maintenance problems relative to excessive wear of the valve seat. When it is necessary to replace the seat it would be desirable, especially with large valves to remove and replace the seat without having to dismantle the entire valve. In addition, as described in certain of my above patents, a sliding action is desirable even in a flap gate or flap valve upon closing to wipe the valve seat, and in the case of a vacuum line, upon opening, to break the vacuum before the flap opens.
Similarly with gate valves, valves are often located on a factory floor where it is difficult to disassemble the valve to replace the seat. Accordingly, it would be desirable to provide a valve in which the seat could be easily removed or replaced and in which the seat could be removed without dismantling the entire valve. Furthermore, even in gate valves it would be desirable to provide a means for clearing the seat surface as the gate closes to minimize wear and to effect a better seal. If particles are lodged between the seat and the edge of the gate, obviously a seal may not be complete and said particles can cause excessive wear in localized areas. In such case then such wear could result in a valve which could not seal so that the seat and/or the gate would have to be completely replaced.